Hi, chadappleguy.
If you're referring to the login picture, this isn't necessarily related to iCloud. In order to change it, follow the steps here:
"Change a user’s login picture on Mac
You can change the picture that appears next to your user name or another user’s name in the login window on your Mac. You can choose a photo from your photo library, take a new photo using the camera on your Mac, choose a Memoji or emoji, use initials in a monogram, and more. Your user login picture is also displayed as your Apple ID picture and as your My Card in Contacts.
- On your Mac, choose Apple menu
> System Preferences, then click Users & Groups 
. - If the lock at the bottom left is locked
, click it to unlock the preference pane. - Select the user account on the left.
- You can’t select an account for a user that’s currently logged in (indicated by a checkmark on the user’s picture). The user must log in and change their picture or log out so you can change it.
- Click the user’s picture on the right, then do any of the following:
- Select a Memoji: Click Memoji, then click the Add button
to select and compose a facial image. Or select one of the displayed Memoji, then select a pose and style you like. - Select an emoji: Click Emoji, then click the Add button to select an image from the emoji library. Or select one of the displayed emoji and select a style.
- Select a monogram: Click Monogram, select a background color, then enter initials.
- Take a picture using your Mac camera: Click Camera. Set up your shot, then click the Camera button. You can retake the photo as many times as you need to.
- Select a photo from your Photos library: Click Photos. To see photos from a specific album, click the arrow
next to Photos in the sidebar, click the album you want, then select a photo. 
- Tip: To quickly replace the current Apple ID picture with an image on your desktop, just drag the image from the Finder onto the current picture.
- Select a suggested image: Click Suggestions, then select a picture.
- After you select an image, you can adjust its look. Do any of the following:
- Adjust the image location: Drag the picture around within the circle.
- Zoom in or out: Drag the slider left or right.
- Click Save.
"
Change a user's login picture on Mac
Cheers.
